Slowly-Varying Forces on Vessels

Abstract

In this paper a method is presented to obtain the slowly-varying force and its spectrum on vessels in irregular beam sea waves. The two-dimensional velocity potential which describes the flow around the vessel in two simultaneous waves is obtained correctly to second order in wave amplitude by means of regular pertubation method. Making use of this result, the slowly-varying force in irregular waves is calculated by direct integration of the hydrodynamic pressure on vessels. The expression of the spectrum of slowly-varying forces is derived from that of the slowly-varying force. Results of computations by present method are exhibited for a shallow-draft barge and compared with the results calculated by Pinkster's approximate method. From the comparison, it is comfirmed that Pinkster's method is not effective in a higher range of circular frequency in some cases.